Can’t recall where, but in last few weeks read something by a supposedly smart Hollywood type, who had been talking to physicists. He said that sound can actually travel faster than light.
The theory he expressed is based on resonance. The assertion is that an object resonates/vibrates instantly through its entire length. So, assuming that the object is subjected to energy that would make it resonate, if the sound caused by resonating occurs simultaneously at both ends, that simultaneous transfer of sound is faster than light, which takes some measurable time to travel the length of the resonating object.
But, is it true that all parts resonate at the same time? For an object to resonate, wouldn’t have to be some way for adjoining molecules to ‘know’ that they were supposed to resonate, implying that there should be a time for the flow of information–which we typically associate with the speed of light. But, since not sure of the mechanism involved in an object resonating along it’s length, have to ask: can this be a way for sound to travel faster than light:confused:?
No. The end. Don’t listen to Hollywood types for science information. Have you ever seen celebrity Jeopardy?
There is one question related to this that smart people sometimes ask. They wonder if you have an extremely long, rigid rod that goes from say the Earth to Mars and you pulled on one end, wouldn’t the pull at the other end be instant and therefore faster than the speed of light? That question has been answered in detail here before but the answer absolutely not. The pull still operates at the speed of sound through whatever solid the rod is made of and is many thousands of times slower than the speed of light.
I think the name “speed of light” is not the best choice overall because it misleads people about what it really is. The speed of light is really the speed limit of the universe known in physics as c. Nothing can transmit information faster than that speed. No one knows why it is the value that it is but it is constant and measurable. There is no need to wonder about tricking light to try to beat c. You can slow light transmission way down in the lab but that has nothing to do with the speed limit of the universe itself. It always stays the same. Light just happens to be one of the things limited by it. Any time someone claims they can beat c itself, you can safely assume they have no idea what they are talking about unless they a world renowned theoretical physicist talking about something bizarre.
This is essentially the same argument as the idea that you could have a rod several light-years long. You then pull on one end, and the other end moves instantly. Unfortunately, they’re incorrect for the same reason. The pull (or resonance) will propagate through the rod at the speed of sound in whatever material it is. This is always less than c.
Basically, smart Hollywood type is full of crap, and not even in an interesting or original way.
And in that case, the ‘something bizarre’ would either be time travel or a complete revamping of physics such that relativity goes out the window. One of those is immediately implied whenever someone claims to be able to transmit information faster than c, and they’re both a lot more interesting than just exceeding that speed limit.
Isaac Asimov covered this thought experiment exactly in one of his non-fiction books about physics. It’s merely people not realizing that pushing/pulling a rod only looks instantaneous at the small, human being size of things. And even then it isn’t (instantaneous). Scale it up to (literal) astronomical sizes and the ‘lag’ of pushing/pulling matter scales up too! Even if you start positing pushing hypothetical rods made of Buckyballs!
An even better ‘faster-than-light?’ scenario Asimov explains away is one that occurred to me as a kid: What if you started rotating a beam of light (i.e. like a laser) faster & faster. Wouldn’t it be fairly easy to get the laser spot traveling faster than light? If the laser was powerful enough that the dot was visible at just over 24½ miles from the source, you’d only have to spin the laser 100 times a second to have the dot go more than 187,000 miles per second (i.e. faster than light).
The flaw is that the ‘dot’ isn’t an ‘object’ ‘traveling’ at all. That’s, again, merely an illusion. Plus, the dot would not be able to even ‘appear’ to move around in a circle faster than light because it still takes time for even the non-corporeal ‘dot’ to go from the source to the ‘wall’. So it would in fact start lagging behind more & more. From above the seemingly perfectly straight laser beam would become a tighter & tighter spiral.
There might well be some substances in which the speed of light is lower than the speed of sound. Generally the speed of sound increases with the density and rigidity of the material. The speed of light, I would think, would fall with the density. The trick probably is to find something that transmits light and does it very slowly. I recall there are some things in which the speed of light has been lowered to a crawl, but I’m not sure if those things transmit sound at all. Of course I suppose one might argue in steel the speed of sound is high and the speed of light is effectively zero.
I covered that in my post earlier. The point is to differentiate the speed of light (meaning c) and not the speed of some beam of light in the lab. The former is a universal constant and the later varies according to the type of light and the experiment but that doesn’t affect c itself.
Incidentally, this shows that there is no such thing as a rigid rod.
There appears to be one way for information to travel faster than c: when you measure the state of one of a pair of entangled particles. However careful analysis has shown that there is no way to use this fact to actually transmit information.
And don’t be too quick to put down Hollywood types. Actress Hedy Lamarr held an important patent for spread spectrum broadcasting during WW II. Beautiful and smart.
Actually, I can think of two situations where sound COULD potentially travel through a medium faster than light.
During a pair instability event, sound would travel faster than gamma radiation travels from the stellar core.
Bose-Einstein condensate should permit sound to travel through, wheras light would be “frozen” under the right circumstances.
But, those are both extremes of physics.